This section is intended to provide a background or context to the invention that is recited in the claims. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived, implemented or described. Therefore, unless otherwise indicated herein, what is described in this section is not prior art to the description and claims in this application and is not admitted to be prior art by inclusion in this section.
The following abbreviations that may be found in the specification and/or the drawing figures are defined as follows:
3GPPthird generation partnership projectAPaccess pointBSbase stationCDFcumulative distribution functionCQIchannel quality indicatorD2Ddevice to deviceDLdownlink (BS towards UE)eNBEUTRAN Node B (evolved Node B)EPCevolved packet coreEUTRANevolved UTRAN (LTE)FDDfrequency division duplexFDMAfrequency division multiple accessLTElong term evolutionMACmedium access controlMM/MMEmobility management/mobility management entityMSEmean squared errorNode Bbase stationOFDMAorthogonal frequency division multiple accessO&Moperations and maintenancePDCPpacket data convergence protocolPHYphysical layerRBresource blockRLCradio link controlRRCradio resource controlSC-FDMAsingle carrier, frequency division multiple accessSGWserving gatewaySINRsignal to interference plus noise ratioSISOsingle input, single outputUEuser equipmentULuplink (UE towards eNB)UTRANuniversal terrestrial radio access network
The specification of a communication system known as evolved UTRAN (EUTRAN, also referred to as UTRAN-LTE or as EUTRA) is currently nearing completion within the 3GPP. As specified the DL access technique is OFDMA, and the UL access technique is SC-FDMA. One specification of interest is 3GPP TS 36.300, V8.6.0 (2008-September), 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (EUTRA) and Evolved Universal Terrestrial Access Network (EUTRAN); Overall description; Stage 2 (Release 8).
FIG. 1 reproduces FIG. 4.1 of 3GPP TS 36.300, and shows the overall architecture of the EUTRAN system. The EUTRAN system includes eNBs, providing the EUTRA user plane (PDCP/RLC/MAC/PHY) and control plane (RRC) protocol terminations towards the UE. The eNBs are interconnected with each other by means of an X2 interface. The eNBs are also connected by means of an S1 interface to an EPC, more specifically to a MME (Mobility Management Entity) by means of a S1 MME interface and to a Serving Gateway (SGW) by means of a S1 interface. The S1 interface supports a many to many relationship between MMEs/Serving Gateways and eNBs.
The eNB hosts the following functions:    functions for Radio Resource Management: Radio Bearer Control, Radio Admission Control, Connection Mobility Control, Dynamic allocation of resources to UEs in both uplink and downlink (scheduling);    IP header compression and encryption of the user data stream;    selection of a MME at UE attachment;    routing of User Plane data towards Serving Gateway;    scheduling and transmission of paging messages (originated from the MME);    scheduling and transmission of broadcast information (originated from the MME or O&M); and    measurement and measurement reporting configurations for providing mobility and scheduling.
The system described above may be referred to for convenience as LTE Rel 8, or simply as Rel 8. In general, the set of specifications given generally as 3GPP TS 36.xyz (e.g., 36.101, 36.211, 36.311, 36.312, etc.) may be seen as describing the entire Rel-8 LTE system.
Of particular interest herein are the further releases of 3GPP LTE targeted towards future
IMT A systems, referred to herein for convenience simply as LTE-Advanced (LTE A). Reference can also be made to 3GPP TR 36.913, V8.0.0 (2008 June), 3rd Generation Partnership Project; Technical Specification Group Radio Access Network; Requirements for Further Advancements for E UTRA (LTE-Advanced) (Release 8).
LTE A will be a radio system fulfilling the ITU R requirements for IMT-Advanced while maintaining backwards compatibility with LTE Rel-8 . It may be assumed at present that single user (SU) MIMO UEs with two or four transmission antennas will be part of LTE A. There are several standards that support D2D operation in the same band as the access point/base station/central controller. However, a common assumption is that the D2D communications occur in separated resources. For example, in HiperLAN 2 (a European alternative to the IEEE 802.11 standards) if one OFDM symbol is reserved for D2D communications, then no other terminal in the same subnet is able to communicate using that OFDM symbol. This restriction ensures that there is no interference from another node in the subnet.
MIMO precoding with feedback from the UE is currently used in LTE for the purposes of enhancing the downlink connection quality and for multi-user MIMO (MU-MIMO). However, currently in LTE there is no support for D2D communications, and hence the feedback mechanisms are not suitable for interference cancellation towards a D2D receiver.
In LTE it is assumed that the UE feeds back information that allows the eNB to enhance transmissions to the corresponding UE.
Stankovic, V. and Haardt, M., in “Generalized design of multi-user MIMO precoding matrices”, IEEE Transactions on Wireless Communications, vol. 7, no. 3, March 2008, propose a precoding scheme for multi-user MIMO applications that is divided into an interference suppression part and a SU-MIMO part. However, this approach is targeted towards MU-MIMO applications. This approach assumes that all terminals are interested in receiving data from the AP, which is not the case in D2D communications. This assumption leads to a different precoder design. Moreover, it does not consider the rank reduction of the effective channel due to receiver processing employed for the reception of the D2D transmission.